1. Field of the Invention
The present invention relates to a dielectric TEM resonator used in a filter or oscillator for radio equipment, and an adjusting method thereof.
The dielectric TEM resonator is used in circuits operating in a several hundred megahertz to several gigahertz band as a compact and low price resonator. As a resonant frequency of the resonator is determined by the effective length of the resonator, some fine adjustments are necessary after incorporation into the circuit. In this specification, a dielectric TEM resonator, wherein these adjustments are easily performed, and a method for adjusting the resonator, are disclosed.
2. Description of the Related Art
A dielectric TEM resonator comprises coaxial inner and outer conductors and a dielectric material filling a space between the inner and outer conductors. At one end of the axially elongated resonator, the resonator is opened and this end of the inner conductor is coupled with other circuit elements. At the other end of the resonator, the resonator is opened to form a .lambda.g/2 type resonator, or is shortened by coupling the ends of the outer and inner conductors in a .lambda.g/4 type resonator.
In both types, a resonant frequency of the resonator is determined by its axial length which is typically determined by the axial length of the dielectric material. Generally, dimensional accuracy of the dielectric material is not satisfactory. Also, effective length of the resonator is affected by the shape of an element coupling the inner conductor with the other circuit elements. Therefore, the resonant frequencies of the resonators must be adjusted in individual products after the resonators are mounted in the circuits.
Conventionally, this adjustment has been performed by shaving off the outer conductor at the open end of the resonator with a file, etc. Having been shaved off, lines of electric force at the open end of the resonator are bent toward the inside, and thus the effective length of the resonator is shortened.
However, the adjustment by shaving-off is not only troublesome, but also has the problem that the resonant frequency can be adjusted only so as to elevate the frequency, and thus inferior products are generated when the resonators are over-shaved.